1. Field of the Invention
The invention relates to a polarized light illuminator in which an alignment layer of a liquid crystal cell element and a wide view film which is built into the liquid crystal cell are irradiated with polarized light.
2. Description of the Prior Art
A liquid crystal cell element is produced as follows:
An alignment layer formed on the surface of a transparent substrate is treated to align the liquid crystals in the desired direction (alignment treatment).
Two of these transparent substrates are cemented to one another such that the alignment layers are located on the inside and a gap with a stipulated distance between the two substrates is maintained.
Liquid crystals are injected into this gap.
For the above described alignment treatment of the alignment layer of a liquid crystal cell element, there is a technique which is called xe2x80x9coptical alignmentxe2x80x9d. Here, an alignment layer is irradiated with polarized light and exposed.
A polarized light illuminator is disclosed, for example, in Japanese patent specification 2928226 and Japanese patent specification 2960392 (both corresponding to published European Patent Application EP 0 913 720 A2 and U.S. Pat. No. 6,190,016).
Recently, the polarized light illuminator has been used more and more often for optical alignment of a wide view film, besides for producing a liquid crystal cell element. A wide view film is produced as follows:
Liquid crystals which can be UV-hardened are applied to the base film.
Liquid crystal molecules are located (aligned) in a certain direction.
Afterwards the liquid crystals are hardened by UV irradiation so that the direction of the liquid crystal molecules is consolidated.
The reduction in image quality can be equalized by cementing a wide view film onto the liquid crystal cell.
The above described alignment process of the xe2x80x9carrangement of liquid crystal molecules in a certain directionxe2x80x9d was conventionally done by rubbing. But recently, more and more often, it is done using the above described illuminator and by optical alignment.
It is necessary for the polarizing device which is used for the above described illuminator to have resistance to heat and strong light. As one such polarizing device, several glass plates are tilted with respect to the optical axis by the Brewster angle and located parallel to one another with distances (hereinafter called a xe2x80x9cpile polarization platexe2x80x9d).
In the aforementioned Japanese patent specifications 2928226 and 2960392, an arrangement is shown in which a pile polarization plate is located in the vicinity of an integrator lens. When the polarizing device is located in the vicinity of an integrator lens, a reduction in size can be achieved more easily than in an arrangement of a polarizing device between the collimator (or a collimator mirror) and a workpiece because the light beam is small in the vicinity of the integrator lens.
However, in the pile polarization plate, it is necessary to increase the number of glass plates which are to be arranged parallel to one another in order to obtain the extinction ratio necessary for alignment of the above described alignment layer. This results in the disadvantages that the costs of the polarizing device increase, that moreover the length of the optical path increases, as is shown in FIG. 9, and that the entire device becomes large.
The invention was devised to eliminate the above described disadvantages of the prior art. As a result, primary objects of the present invention are to reduce the size of a polarizing device used for a polarized light illuminator, to cut the costs of the polarizing device and to reduce the size of the entire polarized light illuminator.
A polarized light beam splitter can be imagined as a polarizing device which has resistance to heat and strong light. A polarized light beam splitter is produced by vacuum evaporation of an inorganic, dielectric, multi-layer film (which serves as a polarization separating film) onto the inclined surface of a right-angled prism, and by cementing the inclined surfaces of two right-angle prisms to one another.
The unpolarized light incident in the polarized light beam splitter is separated into P-polarized and S-polarized light by the inorganic, dielectric, multi-layer film. The P-polarized light propagates in a straight line and is transmitted by the beam splitter. The S-polarized light is reflected. Since the prism is made of quartz glass, it is resistant to heat and strong light.
Since the inorganic, dielectric, multi-layer film which is a polarization separation film made of an inorganic material, it has resistance to heat and strong light. Furthermore, an inorganic, dielectric, multi-layer film can be produced which, at a predetermined wavelength, has a good polarization separation characteristic (which has a good extinction ratio, for example, a small portion of the S-polarized light in the transmitted polarized P-polarized light).
On the other hand, according to the enlargement of the surface of the liquid crystal cell element, the irradiation area becomes larger, by which the device becomes larger and also a large polarizing device is needed. The size of the prisms comprising the polarized light beam splitter is, however, limited for reasons of production, such as due to the size of the vacuum evaporation device which forms the vacuum evaporated film. Furthermore, the costs of the quartz prism become very high when the prism becomes large.
Therefore, a polarizing device is formed by combination of several of these polarized light beam splitters with one another. Thus, combining small prisms yields a large polarizing device. In this way, for example, an application for optical alignment of a large liquid crystal cell element is enabled and the costs can also be reduced. Furthermore, since the length of the polarizing device can be reduced in the direction of the optical axis, the illuminator can be made smaller.
However, if light is incident in a polarizing device which has been formed by combination of several polarized light beam splitters, a shadow forms in the areas of the boundary surfaces of the polarized light beam splitters. When this shadow is projected unchanged onto the irradiation surface, the illuminance is reduced and the distribution of the illuminance on the irradiation surface is degraded.
The objects of the invention are achieved as follows:
(1) In the case of an arrangement of a polarizing device which has been formed by combination of several polarized light beam splitters, on the incidence side of an integrator lens:
The polarized light beam splitters are arranged such that the shadow formed by the areas of the boundary surfaces of the polarized light beam splitters is projected onto the boundary lines between several combined lenses of the integrator lens.
The boundary surfaces between the respective lenses of the integrator lens are shadowy due to light irradiation. However, these shadows are projected onto the outer side of the irradiation area. Therefore, when the shadow of the boundary surfaces of the polarized light beam splitters is projected onto the boundary lines between the respective lens of the integrator lens, the shadows are prevented from being projected onto the irradiation surface by the boundary surfaces of the polarized light beam splitters.
In this way, the reduction in illuminance and the deterioration of the distribution of the illuminance on the irradiation surface by the shadow of the surfaces on which the polarized light beam splitters are combined with one another, i.e., the boundary surfaces, can be prevented.
2) In the case of an arrangement of a polarizing device which has been formed by combination of several polarized light beam splitters, on the outlet side of an integrator lens:
When light is incident on the integrator lens, the illuminance of the light which emerges from the outer peripheral edge area on the respective outlet side of the respective lens of the several lenses which form the integrator lens is reduced more than the illuminance of the light which emerges from the middle area. However, since the light emerging from the integrator lens broadens, on the light irradiation surface, the above described areas in which the illuminance decreases are projected onto the outside of the irradiation area.
Therefore, in the outer peripheral edge area of the respective lens of the above described integrator lens, i.e., in the areas in which the illuminance of the light which emerges from the boundary surfaces of the respective lenses is reduced, there are the boundary surfaces of the polarized light beam splitters.
However, since the light emerges broadened from the integrator lens and the above described areas in which the illuminance is reduced broaden, it is necessary to determine the locations at which the boundary surfaces of the polarized light beam splitters are located according to this broadening.
This can prevent the boundary surfaces of the polarized light beam splitters from being projected onto the irradiation surface. In this way the reduction of illuminance and the deterioration of the distribution of the illuminance on the irradiation surface can be prevented.
(3) The prisms comprising the polarized light beam splitters are joined to one another with xe2x80x9coptical contactxe2x80x9d. An adhesive or a sealant is applied to the vicinity of the joining surfaces.
Usually, an adhesive or sealant is used to cement the inclined surfaces of two right-angled prisms to one another. However, currently, commercial adhesives or sealants absorb UV light and are damaged over time when they are irradiated with UV light with the wavelength which is used for optical alignment (currently with respect to the material for the alignment layer, often with a wavelength from 200 nm to 340 nm). In this way, the transmittance of the UV light is reduced. Therefore, to cement the polarized light beam splitters, an xe2x80x9coptical contactxe2x80x9d is used, and thus, joining takes place, but xe2x80x9coptical contactxe2x80x9d is easily lost by the influences of temperature changes and humidity. In a polarized light illuminator, it is necessary to keep the properties, such as the extinction ratio of the emitted polarized light and the like, stable over a long time. When the adhesive surfaces of the polarized light beam splitters become loose, the polarization characteristic decreases. Therefore, an adhesive or sealant is applied to the vicinity of the cemented surfaces and the humidity is prevented from being absorbed by the inner sides of the adhesive surfaces. Thus, the connection strength is maintained.
The invention is explained in detail below using several embodiments shown in the accompanying drawings.